evaluation of the evaluated data...2012/09/04  · equation) with bolsig+ which is based on the...

Y. Itikawa

At the IAEA Consultants Meeting

7-9 February, 2012, NIFS

my personal experience in data evaluation was reported.

Today

one step further !

There is no standard method of data evaluation.

→

The result of evaluation (i.e., the recommended data) may be different depending on who evaluates them.

We need

evaluation of the evaluated data

Examples of attempt:

(1)Consistency of the total scattering cross section

(2)Swarm parameters

(3)Modelling result

Consistency of

the total scattering

cross section

QT = Σ Qs S= elastic and all inelastic processes

QT can be measured directly.

We can test

QT (measured) = Σ Qs ?

0.01

0.1

1

10

100

cross

sec

tion (

10

-1

6 c

m2)

0.001 0.01 0.1 1 10 100 1000

electron energy (eV)

elas

tot

mom transf

rot J=0 2

v=0 1

ion(tot)

diss

ion(diss)

a

B

C

e + N2

vib v=0 1

e + N2 Itikawa, JPCRD 35, 31 (2006)

Energy (eV) 100 200 500 1000 uncertainty

elastic 5.6 3.5 1.85 1.0 20%

ionization 2.51 2.19 1.36 0.85 5%

dissociation 1.16 0.95 20%

electronic

exc

0.43 25%

sum 9.70 6.64 3.21 1.85

Total

(measured)

8.94 6.43 3.55 2.13 5%

e + N2 (cross sections in 10-16 cm2 )

e + O2 Itikawa, JPCRD 38, 1 (2009)

Energy (eV) 100 200 500 1000 uncertainty

elastic 4.78 3.15 1.72 1.10 20%

ionization 2.43 2.28 1.46 0.922 5%

dissociation 0.33 0.29 34%

electronic

exc

0.41 0.26 0.13 0.08 25%

sum 7.95 5.98 3.31 2.10

Total

(measured)

8.68 6.24 3.58 2.08 5%

e + O2 (cross sections in 10-16 cm2 )

This relation generally holds, when uncertainty of individual cross sections is considered.

Details

We have no data, or less reliable data, for excitation and dissociation.

Furthermore, a part of excitation

contributes to diss.

→ Double counting ?

But contribution of exc & diss to QT is small. It is not a serious problem.

The most serious problem is the uncertainty of elastic cross section.

Can we measure the elastic cross section within an uncertainty of 5% ?

Swarm parameters

Website for

collecting, displaying and

downloading

electron-scattering cross sections

and

swarm parameters

(mobility, diffusion coefficient,

reaction rate etc)

Developed and maintained by

the Toulouse group (L.C.Pitchford et al.)

See

S.Pancheshnyi et al.

Chem. Phys. 398, 148 (2012)

(1)Make an intercomparison of the cross section data sets

(2)Calculate swarm parameters and compare them with experimental values

(with solving the Boltzmann

equation)

with BOLSIG+

which is based on the two-term

approximation of the electron

distribution function

See

Hagelaar and Pitchford

Plasma Sources Sci. Technol. 14, 722 (2005)

All the following figures of swarm parameters are provided by Leanne Pitchford.

0.1 1 10 100

1x1024

1025

Experiments : Nakamura

calculations : Itikawa

µN

(m

. v.

s)-

1

E/N (Td)

N2

1 Td = 10-21 V m2

0.1 1 10 100

0.01

0.1

1

10

calculations

Itikawa data

Expriment

Crompton

Jory

Crompton 1963

townsend

Naidu

Warren

Fletcher

Wedding

DT

/µ (

eV

)

E/N (Td)

N2

0.01 0.1 1 10 100 1000 10000

1x1024

1025

1026

Experiments

Nelson

Pack

Herreng

Nielsen

Fleming

Doehring

Naidu

Fromhold

Schlumbohm

Roznerskhi(below 27.5Td)

Roznerskhi(taken 293K)

Mobili

ty (

/m/V

/s)

E/N (Td)

Calculations

Biagi LXCat and Bolsig+

Phelps LXCat and Bolsig+

Trinite LXCat and Bolsig+

Biagi Monte Carlo

Itikawa No Dissoc LXCat and Bolsig+

O2

0.1 1 10 100 1000

0.1

1

10

Calculations

Biagi LXCat and Bolsig+

Phelps LXCat and Bolsig+

Trinite LXCat and Bolsig+

Biagi Monte Carlo

Itikawa No Dissoc LXCat and Bolsig+

D/

(eV

)

E/N (Td)

experiments

Fleming

Rees

Huxley

Naidis

O2

Mobility and diffusion coeffcient calculated with Itikawa’s cross sections generally agree with the corresponding measured values, except for some discrepancy at high E/N.

A part of electronic-state excitation contributes to dissociation. Can we separate that part ?

In the present calculation, we simply ignore the dissociation process.

We found that

the dissociation has a significant effect in the case of O2,

but much less effect in the case of N2.

Chemical modelling

with reaction rate data

base

A wide variety of molecules have been found in interstellar space

→ (Interstellar) Molecular Cloud

→ Formation of stars

Calculation of synthesis and destruction of interstellar molecules

with solving time-dependent rate equations

→ Molecular abundance (time dependent)

Needs reaction rate coefficients

V. Wakelam et al.,

Space Sci. Rev. 156, 13 (2010)

Reaction Networks for Interstellar Chemical Modelling: Improvements and Challenges

udfa

(The UMIST Database for Astrochemistry)

420 species, 4573 reactions

www.udfa.net

OSU model

(Ohio State University, Astrophysical Chemistry

Group)

468 species, 6046 reactions

www.physics.ohio-state.du/~eric/research.html

KIDA

(Kinetic Database for Astrochemistry)

474 species, 6090 reactions

kida.obs.u-bordeaux1.fr/models

Comparison with observation

Example:

negative ions (recently observed)

using udfa

Observation vs model : Molecular abundance In the circumstellar region IRC+10216

Error bars of calculation are due to the uncertainties in the rate coefficients.

Discrepancy is caused probably by

incompleteness in the chemical network

or

wrong reaction rates of key reactions involving those species

Intercomparison of models

Example

abundances of H3O+, HCO+,

etc

Kida vs OSU vs udfa

Molecular abundances in a dense cloud (T=10 K)

Black dotted lines are 2σ error bars of kida results.

The three different chemical models are consistent with each other, if the uncertainties of the rate coefficients are considered.

But

Quite a small number of reaction processes have measured or calculated rate coefficients at low temperature.

Then many processes have rate coefficients obtained by a combination of experiment, theory and common sense (chemical intuition !).

Any attempt of application of the evaluated data can be a chance of the evaluation of them.

In this sense, comments of users are helpful for evaluation of the evaluated data.

Website of database should have a page for feedback where users can easily contact and send their comments.